Britain has dispatched a search and rescue mission to New Zealand, Prime Minister David Cameron said on Tuesday, to help find survivors of a powerful earthquake that has killed at least 65 people in the second city of Christchurch.

Voicing his "deepest sympathies and condolences" to New Zealand, Cameron said the UK "stood ready" to provide further help at this "dark and difficult time".

"There are many people in Britain with ties of friendship or family to New Zealand," said Cameron, speaking to British journalists travelling with him in Kuwait.